Osprey books can have some really bogus information and interpretations in them, so never take them as gospel. Always confirm with other sources. The go-to book most people recommend for new enthusiasts is Arms and Armor of the Medieval Knight by Edge and Paddock.
Funny you mention that Sir Ian. My history professor gave me that book upon learning about me joining the SCA and it has helped me in my acquisitions tremendously.
Westcoast, as a fellow Scadian from Atlantia I must hail you and congratulate you on joining our cult! I have only been in six months now but it has begun to dominate most aspects of my life. I will hop on board with the others and say functionality should be your chief concern. Looking cool is important in the SCA, it gains respect and admiration in a society where there is a true opportunity for advancement. However, battlefield prowess is of course the name of the game. Here are some armorers I think you should look in to for your 15th century period goals.
Eric Joseph of James River Armoury is down there in Caid as we speak so shipping and acquisitions will be quick with him, however he is moving back here to Atlantia soon so I'd hop on board while you can! You can find him on facebook or on etsy.
Forge Of Svan makes some awesome BOTN gear at an incredibly affordable price but they are in Ukraine.
Steel Mastery is a group from Ukraine, like Forge Of Svan, their main focus is BOTN. Whatever works for ACL and BOTN guys will more than work for SCA use. I've seen some people on this forum gripe about their quality though...and they're undeniably expensive as well.
Mad Matt's Armory is also an affordable and awesome armorer that will cater to you on a personal level. They have some very affordable bascinets on there. If you're going for an SCA legal armet it's going to be hard to find one under 900 bucks. A hounskull or klappvisier serve a similar function but are more affordable.
I look forward to seeing you on the field of battle some day. Hopefully you can make it to this year's Pennsic!